Jacketed discharge lamp



Dec. 12,1967 B. E. SHANKS 73,358,167

JACKETED DISCHARGE LAMP Filed Oct. 18, 1965 lnven tor'.

Bruce E. Shanks b j fi M Q Hi5 A t -tovneg United States Patent Cfi ice 3,358,167 JACKETED DISCHARGE LAMP Bruce E. Shanks, Wicklifle, Ohio, assignor to General Electric Company, a corporation of New York Filed Oct. 18, 1965, Ser. No. 497,405 7 Claims. (Cl. 313-25) ABSTRACT OF THE DISCLOSURE This invention relates to a jacketed elongated low pressure discharge lamp, typically a fluorescent envelope surrounded by a glass sleeve.

The light output of the common fluorescent lamp drops radically under low temperature ambient conditions, particularly when subject to Wind or drafts. The phosphor in a fluorescent lamp is energized by the 2537 A. radiation produced by the discharge through mercury vapor,

and such radiation is a maximum at a mercury'vapor pressure of about 6 microns corresponding to an envelope temperature of about 40 C. By placing a lighttransmitting jacket such as a glass sleeve around the lamp, the heat loss from the lamp is reduced and the light output is maintained at temperatures down to C. or freezing. Such jacketed fluorescent lamps are commercially available and are widely used in exposed outdoor locations during the winter months and in freezer installations. 1

The observation has been made that the commercially available jacketed fluorescent lamps become hard to start when operated in sub-zero temperatures for extended periods of time as in cold storage freezers. This effect is caused by migration of mercury to the ends of the lamp where it condenses due to the lower temperature where the glass envelope is cemented to a conventional base which is exposed to ambient temperature conditions. Upon migration of the mercury to the ends of the envelope, the middle portion of the lamp experiences mercury starvation which causes the lumen output to fall, and the lamp becomes harder. to start. One object of the invention is to provide a base-spacer construction which will remedy this problem.

relationship around the lamp envelope.

In accordance with my invention, I provide a base spacer assembly in a jacketed lamp which supports the jacket directly rather than through the lamp as heretofore. The lamp envelope proper is supported within the base and jacket enclosure by a spacer of thermally insulating material to which the base is also attached. The inlead wires extending from the envelope are connected 3,358,167 Patented Dec. 12, 1967 to the contacts or terminals of the base. When the lamp is turned off, retention of heat by the insulating spacers at the ends of the envelope allows the center of the envelope to cool first so that mercury condensation occurs at the center where it is available for starting purposes. By varying the composition of the insulating spacer to alter the specific heat and thermal conductivity, the rate of mercury condensation in the different areas of the envelope can be predetermined in order to optimize the lamp for various ambient temperature conditions.

In some applications a jacket is desired around a fluorescent lamp to shield against insects and to reduce breakage from flying objects through vandalism. In such case the jacket is preferably made of a high impact strength non-yellowing transparent plastic material such as acrylic or polycarbonate plastic-rather than glass.

Provision may be made to circulate air through the space between jacket and envelope to prevent excessive temperature rise of the envelope When operating under high ambient temperature conditions.

For a better understanding of the features and advantages of the invention, attention is now drawn to the following description of a preferred embodiment to be read in conjunction with the accompanying drawing. The features believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

FIG. 1 is a foreshortened side view of a jacketed fluorescent lamp embodying my invention.

FIG. '2 is an end view of the lamp showing the base or end-cap.

FIG. 3 is a side sectional view of one end of the lamp taken along 33 of FIG. 2.

FIG. 4 is a perspective view of the thermal insulating spacer utilized in the base-spacer assembly of my invention.

Referring particularly to FIGS. 1 and 3 of the drawing, a jacketed fluorescent lamp 10 embodying the invention comprises an elongated discharge envelope 11 and an outer glass sleeve 12 which surrounds and is spaced from the envelope. The glass sleeve 12 encloses an air space which serves to thermally insulate the discharge envelope 11 from external cooling air flow and ambient temperature conditions. Hence, the shielding and insulating effects of the glass sleeve and trapped air on the discharge envelope 11 aid in stabilizing and starting the arcdischarge. Ordinarily the discharge envelope 11 is afluorescent tube in which case the glass envelope is coated on its interior surface with a light-emitting phosphor 14. However, the discharge envelope 11 could be a germicidal lamp finding use in cold storage rooms for controlling or reducing mold formation on meat and foodstulfs. In such a case, the glass sleeve 12 would consist of quartz or an ultraviolet radiation-transmitting glass or other suitable material. Also, the sleeve could be made of a high impact strength non-yellowing transparent plastic material to shield the envelope against insects or objects thrown by vandals.

Regardless of the specific light-emitting source, an arc discharge within the envelopell is initiated and maintained by a cathode 15 mounted on a stem press 16 forming part of a flare 17 heat-sealed to the end of the glass envelope at a juncture forming a bead 17a. Electrical connections to the cathode are made through inleads 18. Starting occurs when the voltage dilference between the cathodes at opposite ends of the envelope is suificient to strike an arc in the filling gas. The discharge current through the mercury vapor causes changes in the energy levels of the electrons in the mercuryions resulting in the release of radiation, mainly ultraviolet at 2537 A.

The fluorescent material subjected to such radiation is caused to fiuoresce and emit visible light. If the mercury vapor condenses in the area of bead 17a, the effective concentration of mercury ions in the arc stream is reduced causing the lumen output to fall and making the lamp hard to start.

This invention provides an improved base-spacer assembly 19 in which the cooling effect on the discharge envelope end (bead 17a area) is minimized and a better and more secure means of supporting the discharge envelope 11 is provided. In this way, the operation of discharge envelope 11 is further stabilized and condensation of mercury at the ends of the glass envelope adjacent the bases is markedly reduced. When the lamp is turned off, the base-spacer assembly retains heat keeping the ends of the envelope warm. As a result, mercury condenses in the cooler center portion of the discharge envelope 11 where it is available for starting.

Base-spacer assembly 19 comprises an annular spacer disc or ring 20 of thermally insulating material and a base or end cap 21. The insulating material is preferably rubber or resilient rubber-like material. The bore 22 of spacer 20 receives the discharge envelope 11, the assembly being shown in FIG. 3 and the spacer alone in FIG. 4. Bore 22 is shaped to limit the ingress of envelope 11 into it in order to avoid any direct contact between lamp envelope and base proper. In the illustrated embodiment, this is accomplished by an internal shoulder 23 formed near the outer end of bore 22 against which the end of envelope 11 adjacent bead 17a rests. Spacer 20 has an annular groove 24 in its inner face. One wall 25 of the groove tapers toward bore 22 and terminates in a knob-like portion 26 which facilitates initial positioning of glass sleeve 12 on the spacer. In the final assembly, glass sleeve 12 is pressed home into groove 24 and the taper in wall 25 assures good frictional engagement and a secure assembly. In addition to positioning glass sleeve 12 as previously explained, knob-like portion 26 serves as a thermal reservoir and its mass may be increased to provide additional insulation of the discharge envelope 11 from the cooling effect of the base. By varying the composition of spacer 20, its specific heat and thermal conductivity can be altered to achieve the required insulation for given ambient conditions.

Base or end cap 21 comprises a hollow body member 27 of electrically insulating material and a skirt-like metal shell 28, suitably of aluminum, whose rim is embedded in the edge of the body member. After assembly, hollow body member 27, metal shell 28, and spacer 20 assume the relative positions shown in FIG. 3. The inner surface of shell 28 grips the peripheral outer edge of spacer 20 and can be formed to press inwardly upon the spacer. By so doing, the resilient material of the spacer ring is placed in compression between shell skirt and sleeve. The sleeve also compresses the spacer ring against the envelope, and the pressure exerted by the shell skirt suffices to relieve tensile stress in the sleeve. Thus all glass parts are in compression, and this is the form of stress in which glass is strongest. Body member 27 contacts the outer face 29 of spacer 20 but is separated from glass envelope 12 by shoulder 23, so that the envelope end is effectively insulated from the base. The engagement of shell 28 with spacer 20 suffices to hold base-spacer assembly 19 together without additional bonding.

Body member 27 has a hollow elongated embossment 30 extending across the center and projecting outwardly for engagement in a lampholder (not shown) and defining a slot 31, as taught in US. Patent 2,922,137Krupp et al. The slot accommodates electrical contacts 32 to which inleads 19 are connected.

In one method'of assembling the jacketed lamp, discharge envelope 11 is nested in glass sleeve 12. Spacer 20 is then brought into position so that bore 22 aligns with envelope 11 which is forced in until it comes to rest on shoulder 23. Simultaneously glass sleeve 12 is forced home in annular groove 24. Base 21 is then brought into position such that body member 27 contacts the outer face 29 of spacer 20 and the inner surface of shell 28 contacts the outer edge of the spacer. The outer cylindrical surface or skirt of shell 28 is then subjected to a compressive force to squeeze it down on spacer 20; this may be done by rolling in the edge of shell 28. Inleads 19 are threaded through bore 22 of the spacer and slot 31 of the base and connected to the electrical contacts 32, suitably by welding as taught in US. Patent 2,749,528Albrecht.

After assembly is completed as described above, head 18 and the entire end of envelope 11 is insulated by the spacer 20 from contact with body member 27 and shell 28 of the base as shown in FIG. 3. Glass envelope 11 is also spaced and insulated by spacer 20 from contact with glass sleeve 12. Thus, the ends of the envelope are thermally insulated from ambient temperature conditions experienced by the exposed portion of the base or end cap, and support of the relatively heavy glass sleeve directly through spacer and base results in a secure and rugged assembly.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A discharge lamp comprising an elongated tubular vitreous envelope having an inlead extending from an end, an elongated radiation-transmitting sleeve surrounding said envelope, a thermally insulating spacer at said end of said envelope, said spacer having a central bore accommodating the envelope end and an annular groove accommodating an end of said sleeve to support the sleeve spaced from the envelope, and a base comprising an electrically insulating body supporting an electrical contact and an annular metal shell attached thereto, said metal shell gripping said spacer to fasten said base to said spacer with said body spaced from the end of said glass envelope, said inlead being connected to said electrical contact.

2. A discharge lamp provided with an elongated glass envelope having inleads extending from its ends, a basespacer assembly at each end of said envelope comprising a thermally insulating spacer ring having a central bore accommodating the end of said envelope, said ring being provided with an annular groove surrounding said bore, an elongated tubular light-transmitting sleeve surrounding said envelope with the end of said sleeve being seated in said groove, said base-spacer assembly including a base comprising an electrically insulating body carrying electrical contacts and an annular skirted metal shell fastened thereto, said metal shell being proportioned to grip the peripheral edge of said ring, said inleads being electrically connected to said contacts.

3. A discharge lamp as defined in claim 2 in which the spacer ring is made of resilient material and is compressed between the glass envelope, the tubular sleeve, and the metal shell.

4. A discharge lamp as defined in claim 2 in which the skirted shell of the base is rolled down on the peripheral edge of the spacer ring.

5. A discharge lamp provided with an elongated glass envelope having inleads projecting from its ends, a spacer ring of thermally insulating material having a central bore accommodating said envelope, said bore having an internal shoulder against which the end of said envelope abuts, the inner face of said ring being provided with an annular groove surrounding said bore, an elongated tubular light-transmitting sleeve surrounding said envelope with one end of said sleeve being seated in said groove, and a base comprising an electrically insulating body member carrying electrical contacts and an annular skirted metal shell fastened thereto, the skirt of said metal shell gripping the peripheral edge of said disc to retain said body against the outer face of said disc and thereby thermally insulate said envelope therefrom, said inleads being electrically connected to the contacts on said body.

6. A discharge lamp as defined in claim 5 in which the spacer ring is made of resilient material and is com 6 pressed between the glass envelope, the glass sleeve and References Cited the metal shell.

7. A discharge lamp as defined in claim 5 in which UNITED STATES PATENTS the spacer ring is made of resilient material and the 1,990,205 2/1935 Reger 31347X skirted shell is rolled down on the peripheral edge of 5 3,179,792 4/1965 Weiss 240-11.4

the spacer ring to compress it against the glass envelope and the sleeve. DAVID J. GALVIN, Primary Examiner. 

1. A DISCHARGE LAMP COMPRISING AN ELONGATED TUBULAR VITREOUS ENVELOPE HAVING AN INLEAD EXTENDING FROM AN END, AN ELONGATED RADIATION-TRANSMITTING SLEEVE SURROUNDING SAID ENVELOPE, A THERMALLY INSULATING SPACER AT SAID END OF SAID ENVELOPE, SAID SPACER HAVING A CENTRAL BORE ACCOMMODATING THE ENVELOPE END AND AN ANNULAR GROOVE ACCOMMODATING AN END OF SAID SLEEVE TO SUPPORT THE SLEEVE SPACED FROM THE ENVELOPE, AND A BASE COMPRISING AN ELECTRICALLY INSULATING BODY SUPPORTING AN ELECTRICAL CONTACT AND AN ANNULAR METAL SHELL ATTACHED THERETO, SAID METAL SHELL GRIPPING SAID SPACER TO FASTEN SAID BASE TO SAID SPACER WITH SAID BODY SPACED FROM THE END OF SAID GLASS ENVELOPE, SAID INLEAD BEING CONNECTED TO SAID ELECTRICAL CONTACT. 